Tall fescue (Festuca arundinacea Schreb.) is a cool season, perennial, sod forming bunch grass grown on over 35,000,000 acres (141,640 km2) (Ball et al., 1993) of pasture and forage land in the United States, including 17 million acres (68,797 km2) in Missouri (Roberts, C. A., 2000), 5.5 million acres (22,257 km2) in Kentucky (Lacefield and Evans, 1984), 1 million acres (4,047 km2) in each Georgia (Hancock, D., 2011), and Indiana (Cherney and Johnson, 1993). Tall fescue supplies most of the nutrients needed by more than 20 percent of United States beef cattle herds (West and Waller, 2007).
In 1931, Dr. Fergus of the University of Kentucky discovered a tall fescue ecotype while visiting the Suiter Farm in Menifee County, Kentucky. After 12 years of testing in Kentucky, the tall fescue cultivar was released as Kentucky 31 in 1943 (Lacefield and Evans, 1984). Most tall fescue, including Kentucky 31, in the United States is infected with a wild-type fungal endophyte, Neotyphodium coenophialum (former known as Acremonium coenophialum) that is toxic to animals, causing a syndrome known as fescue toxicosis or summer slump.
Fescue toxicosis is a disorder of all domestic grazing animals, including; cattle (Bos spp.), sheep (ovis spp.), and horses (Equus spp.) grazing endophyte (Neotyphodium coenophialum) infected tall fescue. Fescue toxicosis can cause decreased weight gain from 30 to 100% for grazing steers (Paterson et al., 1995), decreased milk production (Peters et al., 1992), decreased pregnancy rates (Schmidt et al., 1986), and increased respiration rate, and body temperature (Zanzalari et al., 1989). Fescue toxicosis is one of the most costly animal disorders facing the livestock industry in the eastern United States, affecting over 8.5 million cattle (Ball et al., 2007) and costing the United States beef industry an estimated $609 million annually in lost revenue because of reduced reproductive and growth rates in cattle herds (Hoveland, 1993).
To combat the effects of fescue toxicosis, the first Acremonium coenophialum free tall fescue variety, AU Triumph, was released in 1983. Animal performance was reported to be excellent (Hoveland et al., 1982), with annual forage production equal to or greater than Kentucky 31 (Pedersen et al, 1983). AU Triumph was however reported to be less tolerant to cold, drought, and overgrazing than Kentucky 31 E+ (where E+ means that the variety has a high content of endophyte), resulting in stand losses in overgrazed stressful environments.
Although the wild-type endophyte's toxins cause livestock disorders, infection of tall fescue cultivars with a Neotyphodium endophyte and the resulting host plant-endophyte interactions often results in improved tolerance to abiotic (Arachevaleta et al., 1988) and biotic (Popay and Bonos, 2008) stresses and improved overall persistence of cool-season perennial grasses.
One management strategy for minimizing the effects of tall fescue toxicosis is the replacement of toxic tall fescue with cultivars that are endophyte-free or contain non-toxic endophytes.